A laboratory-scale experimental investigation on the performance of lime columns in expansive Ankara (Turkey) Clay

Swelling of expansive soils and associated movements of foundations cause serious problems to many structures. With the existing expansive clays in Ankara, capital city of Turkey, some light buildings, road pavements and buried pipelines have shown some damage. To avoid such damage, prior to construction expansive clays may be stabilized. There has been little work concerning the stabilization of Ankara Clay and this was concentrated on the lime mixture technique. The main objective of this study was to investigate the performance of the lime column technique on laboratory-scaled models to improve the physical, swelling, strength and consolidation characteristics of this clay. The characteristics of the treated samples were determined in terms of distance to the column and curing period. In general, the results suggested that the most effective zone for the lime migration developed at a distance approximately twice the column diameter and a curing period of 28 days generally seemed to be sufficient. Application of the technique provided a gain in strength between 40 and 80% and resulted in an increase in pre-consolidation pressure and a decrease in the compressibility characteristics of the treated soils, depending on the distance to the lime column. Construction of the column caused a drastic reduction in swell pressure, between 40 and 75%. Electronic Publication     

南宁地区膨胀土膨胀力的现场测试

以广西南宁膨胀土为研究对象,考虑气象因素的影响,进行了现场膨胀力测试。测试场地设置桩和框锚结构,在土体中沿水平方向和垂直方向设置土压力盒,测试浅层土体水平向和竖向膨胀力,膨胀力的测试经历了一个完整的雨季。测试结果表明,土体膨胀力的变化与降雨入渗息息相关,"旱涝急转"的过程会造成土体膨胀力骤然变化,但雨季的持续又会对土体水平向和竖向膨胀力带来不同影响。现场对膨胀土竖向和水平向膨胀力的测试结果可为工程设计的优化提供参考。     

The effect of different types of water on the swelling behaviour of expansive clays

In the design of foundations of structures, especially light buildings, on clayey soils, the main soil behaviours to be considered are swelling properties and surface heave. Therefore, determination of swelling properties by means of swell percent and maximum swell pressure as well as estimation of the surface is very important in the investigation of such soils and light structures on them. In order to obtain the swelling parameters of clayey soils, experimental laboratory tests were carried out and standardised. Distilled water is generally used during these experimental tests; however, the soil in situ interacts with different types of water having different water chemistries. Therefore, the swelling behaviour of expansive soils tested with distilled water would naturally be different from the behaviour of expansive soils tested with different water types and chemistries. For this reason, it was anticipated that determination of the realistic swell behaviour in laboratory experiments requires the use of the same water as in the in situ condition. In this article, the effect of the water type and chemistry on the swelling behaviour of the clays was investigated by testing the clay samples with eight different types of water collected from the sea, river, lake and different rock formations. The main result of this research was that the anticipated clay swell percentages and pressures for different types of water were lower than for the distilled water routinely used in testing.     

宁明膨胀土研究的新进展

广西宁明是著名的膨胀土分布区,20世纪70年代,宁明膨胀土曾造成该区大批工业民用建筑物的严重破坏,对此不少专家、学者曾进行深入的现场调查、变形监测和系统的试验研究。进入新世纪以来随着高速公路建设的迅猛发展,不少公路穿越膨胀土地区,南(宁)友(谊关)高速公路便是其中之一。由于膨胀土对公路的严重危害性以及高速公路对质量的高要求,结合南友路修建,再研究宁明膨胀土工程地质特性及对公路施工和运营的影响有着重要的理论意义和工程价值。另一方面,随着近20年来粘土矿物定量测试技术的进展和膨胀土基础理论研究的深入,再研究在对宁明膨胀土粘土矿物的组成、膨胀土的工程性质与成因关系、膨胀土的干燥活化效应以及改性膨胀土的效果等方面均获得新的进展。     

改进的膨胀土侧限膨胀试验研究

为量测膨胀土在侧限浸水和不同上覆荷载下的竖向膨胀率和侧向膨胀力,通过改进常规侧限膨胀试验装置和方法,确保了施加上覆荷载后试样浸水前初始湿密状态不变,消除了制样产生的初始水平应力,并将侧向膨胀力从总的侧向力中区分出来。采用改进的试验装置和方法,以特定初始湿密状态下的广西百色中等膨胀土为研究对象,分别进行了常规侧限膨胀试验和改进的侧限膨胀平行性试验。试验结果表明:常规侧限膨胀试验中的上覆荷载会改变试样初始湿密状态,测得的竖向膨胀率偏小7%～95%;因制样产生的初始水平应力会使最终侧压力偏小16.1%～43.5%;分级加载和逐级卸载的改进侧限膨胀试验结果具有良好的一致性和可重复性;竖向膨胀率随着上覆荷载逐渐减小,引入相对膨胀率和相对压力,可建立反映极限膨胀状态的幂函数拟合公式;侧向膨胀力与上覆荷载相关并随之增大而逐渐增大,当上覆荷载增至竖向膨胀力时侧向膨胀力达到最大,两者之间可用双曲线较好拟合。研究成果可为膨胀模型的建立以及膨胀土地区支挡结构物设计计算提供参考。     

基于随机场理论的江苏海相黏土空间变异性评价研究

土体空间变异性分析是进行岩土工程可靠度设计的理论基础。采用随机场理论,提出了典型江苏海相黏土的随机场特征及参数,对基于孔压静力触探(CPTU)测试数据的空间变异性进行了系统分析。由于竖直方向上CPTU锥尖阻力数据的样本容量较高,通过对锥尖阻力进行一次多项式去趋势来获得平稳的波动分量,并利用常用的5种自相关模型拟合波动分量的自相关系数。采用修正的Bartlett统计公式来检验波动分量的平稳性,选取最优的竖直波动范围。竖直变异系数由波动分量和去趋势函数来确定。鉴于水平方向上的CPTU锥尖阻力数据的样本容量较小,采用平均零跨距法估计水平波动范围,水平变异系数由总体变异系数来表示。结果表明,竖直向和水平向上江苏海相黏土较报道值显示出更强的空间变异性。     

基于电阻率法的膨胀土吸水膨胀过程中结构变化定量研究

针对非饱和黏性土结构定量研究中存在的困难以及现有的土的结构性研究方法所存在的不足,引入能同步反映土的微结构变化的电阻率方法,探讨土的电阻率方法在黏性土微结构定量研究中的应用。通过膨胀土击实样的无荷膨胀试验,同步测定土样的竖向电阻率与横向电阻率,计算出土的电阻率结构性参数指标,包括土的竖向与横向结构因子、平均结构因子、各向异性系数与平均形状因子的大小,通过研究土样吸水膨胀过程中的土的电阻率结构性参数指标的变化规律,建立描述膨胀土微结构变化的电阻率评价方法。试验结果表明,土的电阻率方法具有连续、快捷与测试方便等优点,其结构性参数指标可有效用于土的微结构变化定量研究。     

Engineering characteristics of a glacio-lacustrine clay deposit in a semi-arid climate

Parent material composition, particle disintegration by glaciers and lacustrine environment govern the geological development and engineering characteristics of clay deposits in southern Saskatchewan. The pre-existing expansive clay minerals were preserved due to the restrained leaching in the Regina Lake and the prevalent aridity in the area. The main objective of this paper was to develop a fundamental understanding of the clay deposit for the use in the design and construction of civil infrastructure. The results indicated the presence of expansive clay minerals in the deposit, with smectite accounting for 35% of the material. The major exchangeable cation was found to be Ca²⁺ which accounted for more than half of the total measured cation exchange capacity of 40 (cmol(+)/kg). The most likely exchange complex governing water adsorption of the clay was determined to be Ca²⁺-smectite. Alongside a high initial saturation (86%), this complex resulted in moderate volume changes in the clay. The swelling pressure was fully developed within the first hour of the constant volume test. The corrected swelling pressure was determined to be 120 kPa leading to an estimated heave of 36 mm in the surface layer of the deposit. The compression index and the swelling index were found to be 0.25 and 0.08, respectively.     

Combined loading of strip footings on sand-over-clay with layers of varying extents

This study describes the numerical analyses performed to investigate the bearing capacity of strip footings placed on granular (frictional) material overlying soft clay subjected to combined vertical-horizontal and vertical-moment loading. A plane-strain finite element limit analysis is used to estimate the limiting load combinations for two layer soil geometries where the top layer is either fully extended in the horizontal direction or it is of limited horizontal extent, representative of rock or gravel berms commonly used in offshore practice.Bearing capacity envelopes for combined vertical, horizontal and/or moment loading are well-documented in the literature for cases of footings resting on single sand or clay soil. For two-layer sand-over-clay soil with a horizontally extensive top layer, the vertical-horizontal and vertical-moment envelopes initially coincide with the envelope for a single sand layer at low vertical loads, but show an abrupt reduction in the horizontal or moment capacity as the vertical load increases beyond a certain critical vertical load. The critical vertical load is found to vary as a function of the thickness and the lateral extent of the upper layer. Relationships are presented to enable the vertical-horizontal and vertical-moment envelopes to be estimated based on the problem geometry and material properties.The findings in this study provide insight into the response of subsea foundations placed on rock or gravel of limited extent overlying a clay seabed as well as the general response of shallow foundations on two-layer profiles.     

膨胀土引起的地面上抬变形及在场地评估中的应用(英文)

回顾了预示膨胀土引起的地面上抬变形的方法和含膨胀土层场地的评估。基于软化模型提出了一个地面上抬变形的计算方法及其公式。给出了确定半空间无限体中土单元在自重下的膨胀势的关系式。对该含膨胀土层的水平场地的地面上抬变形计算方法做了详细说明。对一个含高膨胀压力的膨胀土层的场地计算了地面上抬变形 ,以说明膨胀层位置及厚度对地面上抬变形的影响。最后 ,将该地面上抬变形方法应用于含膨胀土层场地的评估 ,并以例显示了膨胀土层厚度和位置对场地评估的重要影响。     

铁路路基下膨胀土地基浸水响应现场试验

在工程建设中,膨胀土大都属于非饱和土范畴。对高速铁路无砟轨道路基而言,膨胀土的胀缩变形可能加剧线路的不平顺性,影响高速铁路的正常运营。为研究铁路路基荷载下非饱和膨胀土土层在人工浸水后的变形特征,结合云桂铁路建设,设计并开展了铁路原型路基荷载下膨胀土地基现场浸水试验,并监测了从路基填筑开始到人工浸水结束时膨胀土地基与路基本体变形及浅层土水分的时程变化。试验结果揭示了膨胀土地基浸水饱和后的极限相对膨胀量、膨胀变形沿路基横向与地基深度的分布规律以及地基表面膨胀变形沿路基本体的衰减特征。基于试验成果,初步提出了以路基表面膨胀变形为0作为控制标准确定路基临界填高的设计思路。现场试验的设计原则与实施方法也可为今后研究铁路路基下膨胀土地基胀缩特性提供参考。     

击实膨胀土的循环膨胀特性研究

主要研究了干湿循环对击实膨胀土胀缩特性的影响。研究结果表明,击实膨胀土的胀缩变形并不是完全可逆的,随干湿循环的发展,膨胀土的膨胀速率加快,绝对膨胀率总是增大而相对膨胀率则降低。这种变化在第Ⅱ、Ⅲ级循环时最明显,第Ⅲ级循环后便趋于稳定。这些变化特性主要是粘粒集聚、微结构改变的结果。     

Experimental study on seismic performance of prefabricated rocking wall frame structure

为避免罕遇地震作用下传统混凝土摇摆墙的开裂损伤且充分利用装配式结构的便捷性，设计了采用双层钢板混凝土墙的摇摆墙结构体系，在浇筑混凝土时双层钢板可充当摇摆墙构件的外模板。跨越结构上、下层的摇摆墙之间采用高强螺栓连接，摇摆墙在工厂预制后运到施工现场进行安装。选用金属阻尼器作为耗能连接件连接摇摆墙与主体框架结构，同时传递层剪力并耗散地震能量。为研究该装配式摇摆墙-框架结构的抗震性能，设计并制作了一个纯框架和两个摇摆墙-框架，其中两个摇摆墙-框架的区别在于金属阻尼器的安装位置不同。通过拟静力试验分析了其破坏模式及抗震性能。试验结果表明：预制装配式摇摆墙与主体框架结构协同工作性能良好，金属阻尼器耗能效果得到充分利用，结构承载力、耗能能力大幅增加；在水平位移较大时摇摆墙竖向发生刚体位移，对整体结构的抗震性能产生一定影响，后续将采用附加预应力的形式减轻摇摆墙竖向抬升的影响。     

Prediction of lateral swelling pressure behind retaining structure with expansive soil as backfill

Lateral swelling pressure (LSP) develops in expansive soil when the volume expansion associated with water infiltration is restrained in the horizontal direction due to a rigid infrastructure. Various types of testing techniques, used to determine the LSP from both laboratory and field studies, are critically reviewed by focusing on two key factors, namely, the boundary conditions and the saturation path. Most testing techniques are capable of reasonably simulating the stress state of a soil element behind a retaining structure by applying a fixed boundary condition in the horizontal direction and a stress boundary condition in the vertical direction. However, they are only used to determine the LSP following a simple path, which is from an initially unsaturated state to a fully saturated state. In other words, these tests fail to provide information on the variation in LSP with respect to changes in the degree of saturation, the water content or the matric suction during the infiltration process. Furthermore, the literature review suggests that a reliable model for the prediction of the LSP during the infiltration process is not available. For this reason, a model is proposed in this paper to estimate the lateral earth pressure (LEP) considering the variation in LSP behind fixed rigid retaining structures with respect to the matric suction during the infiltration process. The proposed model is simple and only requires information, which includes the soil water characteristic curve (SWCC) and a limited number of soil properties. Data from one large-scale model test and two field case studies from published literature are used to illustrate and verify the proposed model. Reasonable comparisons are made between the predictions and the measured data. The proposed model will be a valuable tool for use in conventional engineering practice for the quick prediction of the increasing LEP behind retaining structures with expansive soils as backfill due to the development of LSP associated with water infiltration.     

Experimental studies on the weatherability of the capivara dam basalts,rio paranapanema,brazil

The weatherability of the basalts in the Capivara Dam site, Rio Paranapanema, São Paulo State, Brazil, has been studied by means of saturation-drying tests. A great number of samples have disaggre — gated intensively with production of fines. The behavior of these rocks is related to their petrography, especially to their content in expansive clay minerals. These studies were performed in order to obtain data for the utilization of this material as rock fill, including ripraps.     

装配式摇摆墙-框架结构抗震性能试验研究

为避免罕遇地震作用下传统混凝土摇摆墙的开裂损伤且充分利用装配式结构的便捷性,设计了采用双层钢板混凝土墙的摇摆墙结构体系,在浇筑混凝土时双层钢板可充当摇摆墙构件的外模板。跨越结构上、下层的摇摆墙之间采用高强螺栓连接,摇摆墙在工厂预制后运到施工现场进行安装。选用金属阻尼器作为耗能连接件连接摇摆墙与主体框架结构,同时传递层剪力并耗散地震能量。为研究该装配式摇摆墙-框架结构的抗震性能,设计并制作了一个纯框架和两个摇摆墙-框架,其中两个摇摆墙-框架的区别在于金属阻尼器的安装位置不同。通过拟静力试验分析了其破坏模式及抗震性能。试验结果表明：预制装配式摇摆墙与主体框架结构协同工作性能良好,金属阻尼器耗能效果得到充分利用,结构承载力、耗能能力大幅增加;在水平位移较大时摇摆墙竖向发生刚体位移,对整体结构的抗震性能产生一定影响,后续将采用附加预应力的形式减轻摇摆墙竖向抬升的影响。     

Landfill site selection utilizing TOPSIS methodology and clay liner geotechnical characterization: a case study for Ankara,Turkey

The purpose of this study was to select alternative landfill sites for Ankara based on the growing trends of Ankara toward the Gölba?? municipality, and to eventually select the best alternative through the use of decision-making tools. Geographic information systems (GIS) and multi-criteria decision analyses were employed to perform landfill site selection. Several criteria, including geology, slope, proximity to roads, availability and proximity of landfill containment material, settlement, suitability for agriculture, vegetation cover, erosion, and lineament system were gathered in a GIS environment. A weight value was assigned to each criterion by applying the pairwise comparison method and the analytical hierarchy method. An ideal point method, namely, the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) was applied to choose the best alternative landfill site. The geotechnical properties of “Ankara clay”, which shows widespread distribution in Ankara, were reviewed and assessed for the clay's suitability as a single, compacted clay liner and as a component of a geomembrane-compacted clay composite liner for the alternative landfill site selected. The HELP model was employed in order to determine the cumulative, mean leachate head and cumulative, unitized expected leakage rate amounts through the landfill. Four different profiles, from the least conservative to the most conservative, were created and analyzed.     

桩板墙地震动力特性的大型振动台模型试验研究

 通过1个比尺1∶8的二级支护边坡大型振动台模型试验,研究地震条件下桩板式挡墙加速度、动位移和动土压力等的响应特性,模型试验以汶川波、大瑞人工波和Kobe波3种地震波作为振动台激振波,汶川波采用水平(X)向、竖直(Z)向和水平竖直(XZ)双向3种激振方式,大瑞人工波和Kobe波采用水平竖直(XZ)双向1种激振方式,研究地震波作用方向和方式以及地震波形等地震动参数对桩板式挡墙地震动力响应特性的影响规律。研究表明：桩板式挡墙加速度、动位移和动土压力等的响应特性,主要受水平向地震波作用的影响,且与地震波类型、激振方向和方式以及测点位置有关。加速度动力响应峰值呈现出沿墙高非线性增大的特征,因而在采用拟静力法时,有必要在考虑支挡结构组合方式、边坡特性及地震波作用方式等影响的基础上,采用合适的地震荷载拟静力值的放大系数。动位移响应峰值和永久位移值呈现出非线性响应特性,水平竖直(XZ)双向地震波激振下,桩板墙主要产生离开土体向边坡外侧平移的动位移模式。动土压力响应峰值沿墙高呈现出两头小中间大的非线性分布特征。     

刚性挡土墙地震失效模式的数值研究

采用离散元方法建立了某刚性重力式挡土墙的数值模型,并根据室内材料试验结果标定了数值模型的微观参数,使数值模拟结果建立在可靠的参数选择基础上。利用颗粒流软件的微观实时测量优势研究了地震荷载作用下挡土墙的失效模式。研究结果表明:加载初期,挡土墙在墙后动土压力、自身地震惯性力和基础摩擦力的作用下保持稳定;随着加速度峰值的增大,动土压力的波动偏离静土压力并逐渐增大,挡土墙发生水平滑移和旋转,当基础破坏后挡土墙还将发生竖向位移。     

组合式挡墙的基坑围护非线性的空间设计计算理论和方法

组合式挡墙的基坑围护能够充分发挥各种型式挡土墙的优点,使基坑围护既安全又经济.本文提出组合式挡墙的基坑围护非线性的空间设计计算理论和方法.工程实例的计算和分析表明,采用这种计算方法计算得到的结果符合实际情况,而计算时间又短,这为组合式挡墙的基坑围护设计计算提供有力的计算手段.